A post-mortem examination of Amerman Racing Stable's Grade 1 winner Siphonic confirmed that the former classic candidate suffered cardiac arrest when he died minutes following his second-place finish in an allowance/optional claiming race at Santa Anita Park on Wednesday.

The Kentucky-bred son of Siphon (Brz) finished a head behind Resolve in the seven-furlong event, then collapsed twice about 15 minutes after the race in the receiving barn.

"The results didn't show anything peculiar physically," trainer David Hofmans said. "It looks like he came out of that race and his heart just gave out. We're still waiting on some soft tissue results that might give us an exact reason.

"It's just unbelievable," Hofmans continued. "We were so happy with the race. He didn't seem too tired coming out of it, and he was cooling down fine."

Siphonic was coming off a nearly seven-month layoff since an injury to his right front ankle was discovered after his win in the San Felipe Stakes (G2) on March 17, sidelining him from the spring classics. He won three of seven career starts in two seasons, including the Lane's End Breeders' Futurity Stakes (G2), and earned $774,778. –Jeff Lowe